1. Field
The invention pertains to systems and methods of minimizing evaporative losses of liquid hydrocarbon fuels from fuel tanks installed on motor vehicles.
2. State of the Art
Asphalt pavement can become considerably hot, up to temperatures of 130.degree. F. to 150.degree. F. during a summer day. The hot, black asphalt transfers heat to all vehicles passing over the pavement. The fuel tanks on the vehicles are customarily installed on the undercarriage of the vehicle, and the surfaces of the fuel tanks which face the pavement receive heat from the pavement by radiation and convection. The same surfaces of the tanks also receive reflected solar radiation from the pavement. As heat is transferred to the fuel tank, the fuel is heated and evaporation increases.
Various systems of venting evaporized fuel have been developed in the prior art and incorporated on motor vehicles. Included among these venting systems are vented tank caps, vents directly to the atmosphere at the top of the tanks, and vents from the top of the tanks to vapor condensation chambers, the carburetor, or vapor absorbtion canisters. The use of fuel tanks which are made to withstand a slight pressure has been used sparingly. The reason pressurized fuel systems have not been utilized more extensively is because they are very ineffective due to the high vapor pressures of the hydrocarbons in the fuel. To be effective, at least with respect to reducing vapor losses, the fuel tank and related system would have to withstand pressures of 35 psi gage or greater.
Fuel vapor storage canisters have been used recently. They are designed to capture and store fuel vapors that escape from the fuel tank while the engine is not in operation. Theoretically, the vapors are to be absorbed on a porous media in the canister. The condensed vapors are to be drawn into the carburetor during subsequent operation of the engine. Unfortunately, however, the capacity of the canisters is much smaller than the amount of vapors which are generated during a typical hot, summer day.
3. Objectives
The principal objective of the present invention is to provide a method of minimizing evaporative losses of liquid fuels from fuel tanks installed on motor vehicles. In particular, it is an objective of this invention to provide a method of effectively minimizing the amount of vaporization occuring within the fuel tanks rather than attempting to recover the unmanageable vapors after they have been generated.